US5645773A - Method for placing concrete for construction of a master concrete structure - Google Patents

Method for placing concrete for construction of a master concrete structure Download PDF

Info

Publication number
US5645773A
US5645773A US08/483,416 US48341695A US5645773A US 5645773 A US5645773 A US 5645773A US 48341695 A US48341695 A US 48341695A US 5645773 A US5645773 A US 5645773A
Authority
US
United States
Prior art keywords
concrete
stress
crack
temperature
predicted
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
US08/483,416
Other languages
English (en)
Inventor
Yasuaki Ichikawa
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
E R C Co Ltd
Original Assignee
E R C Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by E R C Co Ltd filed Critical E R C Co Ltd
Assigned to E.R.C. CO., LTD. reassignment E.R.C. CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ICHIKAWA, YASUAKI
Application granted granted Critical
Publication of US5645773A publication Critical patent/US5645773A/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04G—SCAFFOLDING; FORMS; SHUTTERING; BUILDING IMPLEMENTS OR AIDS, OR THEIR USE; HANDLING BUILDING MATERIALS ON THE SITE; REPAIRING, BREAKING-UP OR OTHER WORK ON EXISTING BUILDINGS
    • E04G21/00—Preparing, conveying, or working-up building materials or building elements in situ; Other devices or measures for constructional work
    • E04G21/02—Conveying or working-up concrete or similar masses able to be heaped or cast
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04G—SCAFFOLDING; FORMS; SHUTTERING; BUILDING IMPLEMENTS OR AIDS, OR THEIR USE; HANDLING BUILDING MATERIALS ON THE SITE; REPAIRING, BREAKING-UP OR OTHER WORK ON EXISTING BUILDINGS
    • E04G21/00—Preparing, conveying, or working-up building materials or building elements in situ; Other devices or measures for constructional work
    • E04G21/02—Conveying or working-up concrete or similar masses able to be heaped or cast
    • E04G21/04—Devices for both conveying and distributing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/72—Investigating presence of flaws

Definitions

  • This invention relates to a method for placing concrete to construct a massive concrete structure such as a dam, a bridge pier or a foundation of a building, and more particularly to a method for placing concrete which prevents formation of cracks in the concrete.
  • a major concern relates to a rise in temperature of the structure.
  • Temperature variation of the structure is caused by a combined effect of (a) heat generation by hydration of cement and (b) seasonal and daily change in temperature of the atmospheric air.
  • hydrating heat may cause a temperature rise of about 15° to 25° Celsius.
  • Most of the stresses to which the concrete structure under construction is subjected during such a temperature rise are compressive stresses.
  • the levels of these compressive stresses are negligibly small and, therefore, the modulus of elasticity is also small and the concrete shows creep behavior.
  • the concrete structure After reaching its peak temperature, the concrete structure starts to cool down. Since the concrete has developed reasonable elastic properties by that time, a high level of tensile stress is observed in the concrete due both to a constraint by a rock foundation (which is called a "foundation constraint effect” or an “external constraint effect”) and to a constraint by the concrete itself (which is called an "internal constraint effect").
  • the temperature of the underlying concrete is equal to the atmospheric temperature and, therefore, the temperature distribution of a completed large-size concrete structure exhibits a periodic profile in its vertical direction, because of the long time required to complete such a large-sized structure, and because the atmospheric temperature naturally varies periodically during construction of the structure.
  • an adequate construction method may be used for suppressing the temperature rise as much as possible. For example, one may reduce the quantity of cement used, may place concrete in half lifts, or may use a pipe cooling or pre-cooling technology.
  • a contraction joint may be provided in advance, at locations where cracks are projected to develop.
  • a proper design or construction procedure may be used to prevent crack initiation in the concrete.
  • the concrete layer adjacent the rock foundation which will be strongly constrained by the rock, may be placed in a season having relatively lower temperatures.
  • the placed layer of concrete when still at a height level lower than the final design height, should not be exposed for a long time.
  • the surface of the placed concrete should be adiabatically cured to prevent a rapid temperature change.
  • the concrete can be placed with appropriate consideration of its creep characteristics.
  • Stress may be estimated by using the concept of constraint factor, as follows: Let R be a constraint factor of a rectangular concrete block placed on a rock foundation. Stress is determined as a function of the geometry and material properties of both of the massive concrete structure and of the rock foundation. The factor is typically given in the form of a graph or a chart. Then, the horizontal stress ⁇ is calculated as
  • E c is the elastic modulus of concrete
  • ⁇ c the thermal expansion coefficient of concrete
  • This procedure for stress estimation is based on an assumption that a rectangular-shaped concrete block is placed on a semi-infinite layer, and that a uniform temperature drop AT will occur in the block. Therefore, with this procedure it is impossible to calculate the stress that will occur in each layer formed under an atmospheric temperature which changes from season to season.
  • the present invention overcomes the difficulties of the prior art, by providing a novel method for placing concrete in design and construction of a massive concrete structure.
  • it is possible to calculate an accurate distribution of stress that will develop in the concrete.
  • the invention thus makes it possible to use a thermal stress control technique. That is, simply by heating or cooling the concrete in the vicinity of the portion which has been predicted to become over-stressed, the invention makes it possible to maintain the stress in the concrete below a maximum level (at which cracks would develop) during and after construction.
  • This technique, for heating/cooling portion(s) of the concrete is very effective in terms of design of massive concrete structures. Indeed, it is possible to introduce a heat pump system for the partial heating/cooling concept of the invention.
  • the invention provides a method for placing concrete to construct a massive concrete structure, such as a dam, a bridge pier or a concrete foundation for a building, which includes: (a) determining a temperature influence function from which one can calculate a thermal stress distribution that will occur in the concrete and which will vary with temperature change; (b) predicting the location at which a crack will develop by using the temperature influence function and a function of thermal change in the concrete; (c) (partially) heating/cooling the vicinity of the predicted location and redistributing excess stress which would cause cracking in the concrete; and (d) reducing the thermal stress in the concrete by transferring the excess heat generated in the concrete structure to a desired location in the concrete which is predicted not to crack.
  • a heat pump system should preferably be employed in implementing step (d). Further, step (a) is preferably implemented by using results of a numerical analysis rather than using the conventional concept of a constraint factor.
  • FIG. 1 shows a typical massive concrete structure having a plurality of layers
  • FIGS. 2(a) and 2(b) show a temperature influence function used for the invention
  • FIG. 3 shows an influence matrix of thermal stress used for the invention
  • FIGS. 4(a)-4(c) show how a temperature influence function and a function of temperature change in the concrete can be used for the invention
  • FIGS. 5(a)-5(c) show how stress can be redistributed by partial heating in accordance with the invention.
  • FIG. 6 shows a heat pump system that can be used to transfer excess heat generated in one portion of a concrete structure to another desired portion.
  • the elements A ij of the influence matrix describe an influence of a temperature change ⁇ T j , in a j-th layer of the concrete structure, to the stress ⁇ i in an i-th layer of the structure.
  • the influence matrix [A] is a function both of the geometry and of the material properties of the concrete structure and the rock foundation.
  • a numerical method such as a finite or boundary element method, is used to specify the influence matrix.
  • the stress ⁇ is a second order symmetric tensor with 3 by 3 components, so the influence matrix may be specified in correspondence to each stress component.
  • the stress component in the horizontal direction is considered to be dominant in the massive concrete problem under consideration, as such a structure has horizontal concrete layers placed on a horizontal foundation.
  • the following describes how the concept of temperature influence function may be used to calculate a stress distribution in a concrete structure. Based on this concept, one can determine the characteristic profile of stress distribution in any structure.
  • the following example provides a method for constructing a concrete structure having a rectangular shape, with a height H and a width B, placed on a horizontal rock foundation as shown in FIG. 2(a).
  • the temperature influence function for such a structure is determined as follows.
  • an observational point (or layer at which the stress is to be calculated) may be in the bottom layer. 2)
  • the values of a row of elements of the temperature influence matrix of FIG. 3, corresponding to the designated observational layer (the bottom layer), are divided by the thickness d of each layer, and then the values are plotted at each layer as shown in FIG. 2(b).
  • a function f(y) which is obtained by smoothing the plotted points as shown in FIG. 2(b), is the temperature influence function of the corresponding observational point (e.g., the bottom layer in FIG. 2(b)). It is noted that +y is the vertical upward direction.
  • the function f is specified as three separate parts.
  • a first part of the function f (a function f 1 ) describes the temperature influence in an upper part of the structure, above the observational layer.
  • a second part of the function f (a function f 0 ) shows the value of the temperature influence in the observational layer, and is in fact a constant.
  • a third part of the function f (a function f 2 ) describes the temperature influence in a lower part of the structure, below the observational layer.
  • the functions f 1 and f 2 may preferably be approximated in a simple form, such as a piece-wise linear or parabolic function.
  • the determined stress distribution is a function both of the temperature distribution T(y) and of the temperature influence function f(y). Accordingly, the inventive approach makes it possible to control excess stress by considering the configurations of either T(y) or f(y).
  • FIG. 3 provides a temperature influence matrix of the stress ⁇ , obtained by a finite element analysis under a plane strain condition.
  • the conditions of the analysis are as follows.
  • the structure is of a rectangular shape with the following dimensions:
  • FIG. 3 the concrete structure is divided along horizontal lines into 25 layers, with a bottom layer numbered "1", a second layer from the bottom layer numbered "2”, and so on. The topmost layer is numbered "25".
  • the coefficients corresponding to the rock foundation are omitted from FIG. 3.
  • FIG. 5(b) For purposes of illustration, the elasticity modulus and Poisson's ratio are assumed to be constant. Under these assumptions, FIG. 5(b) indicates that the peak stress is developed at a layer located at one fourth of the full height of the structure, i.e., one fourth the structure's height above the surface of the foundation rock. This peak stress may be reduced to an acceptable level by heating the concerned layer and the vicinity thereof. Thus, as shown in FIG. 5(c), additional stress can be supplied by such heating.
  • the stress profile for the added stress is indicated by a dashed line in FIG. 5(b), and the combined stress, showing the effects of the added stress, is then reduced to a level indicated by a thick solid line of FIG. 5(b).
  • the excess stress is now redistributed to the entire structure, so that the overall stress in the structure is reduced by the inventive method to a level below the level at which cracks might develop. It should be noted that, since the stress acting on the structure changes with time, an adequate amount of heat must be supplied at the proper time and place.
  • FIG. 6 represents a heat pump system for transferring excess heat generated in one portion of the concrete structure to any other desired portion of the structure, which is at a lower temperature.
  • a heat pump system should preferably be used for implementing the inventive concept of partial heating/cooling.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Architecture (AREA)
  • Structural Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Civil Engineering (AREA)
  • Ceramic Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Health & Medical Sciences (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • On-Site Construction Work That Accompanies The Preparation And Application Of Concrete (AREA)
  • Bridges Or Land Bridges (AREA)
US08/483,416 1994-11-30 1995-06-07 Method for placing concrete for construction of a master concrete structure Expired - Fee Related US5645773A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CN94112848.2A CN1125801A (zh) 1994-11-30 1994-11-30 控制大体积混凝土结构物温度应力的混凝土浇筑方法
CN94112848.2 1994-11-30

Publications (1)

Publication Number Publication Date
US5645773A true US5645773A (en) 1997-07-08

Family

ID=5036426

Family Applications (1)

Application Number Title Priority Date Filing Date
US08/483,416 Expired - Fee Related US5645773A (en) 1994-11-30 1995-06-07 Method for placing concrete for construction of a master concrete structure

Country Status (2)

Country Link
US (1) US5645773A (zh)
CN (1) CN1125801A (zh)

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6286271B1 (en) 1999-05-26 2001-09-11 Carl Cheung Tung Kong Load-bearing structural member
CN102094528A (zh) * 2010-12-09 2011-06-15 中国葛洲坝集团股份有限公司 一种大体积混凝土冷却水管布置方法
CN102134911A (zh) * 2011-04-27 2011-07-27 河海大学 一种计算大体积混凝土水管冷却温度场的方法
JP2013023897A (ja) * 2011-07-20 2013-02-04 Kajima Corp コンクリートの養生方法
US20130269286A1 (en) * 2010-06-14 2013-10-17 Max Bögl Bauunternehmung GmbH & Co. KG Tower of a Wind Power Plant and Method for Producing a Tower of a Wind Power Plant
CN103410148A (zh) * 2013-05-29 2013-11-27 中建保华建筑有限责任公司 一种应用于基础底板混凝土浇筑的拦截网及其施工方法
CN104131563A (zh) * 2014-07-30 2014-11-05 葛洲坝集团试验检测有限公司 一种大体积混凝土消应控制裂缝方法
CN105117567A (zh) * 2015-09-25 2015-12-02 福建江夏学院 一种新老混凝土黏结约束收缩有限元模型的构建方法
JP2018071217A (ja) * 2016-10-31 2018-05-10 鹿島建設株式会社 コンクリートの打設方法
CN108446438A (zh) * 2018-02-09 2018-08-24 广西交通科学研究院有限公司 刚构-拱组合桥成桥最优索力确定及快速实现方法
CN108981966A (zh) * 2018-07-02 2018-12-11 雷元新 一种大体积混凝土温度梯度限值分析方法及装置
CN109056732A (zh) * 2018-09-18 2018-12-21 中水北方勘测设计研究有限责任公司 一种严寒地区混凝土高拱坝的温控方法
CN111460545A (zh) * 2020-03-11 2020-07-28 华中科技大学 一种高效计算超高层结构温度应变的方法和系统
JP2020133102A (ja) * 2019-02-12 2020-08-31 りんかい日産建設株式会社 コンクリート打継部の評価方法および評価装置
CN112685818A (zh) * 2020-12-29 2021-04-20 武汉大学 混凝土拱坝坝体优化方法

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100451245C (zh) * 2007-06-08 2009-01-14 清华大学 普通型堆石混凝土施工方法
CN101358897B (zh) * 2008-08-08 2010-06-02 重庆交通科研设计院 桥梁结构影响线无线遥测自动测试装置
CN104563120B (zh) * 2014-10-29 2017-12-15 中铁三局集团有限公司 隧道溶洞超大体积混凝土分层分区增设矩形预留孔浇筑施工方法
CN105544578B (zh) * 2015-12-18 2017-11-17 中冶建筑研究总院有限公司 一种确定大体积混凝土结构施工养护方法的方法
CN106844990B (zh) * 2016-12-15 2019-08-09 中国水利水电科学研究院 大体积混凝土基础温差应力和上下层温差应力估算方法
CN110820747B (zh) * 2019-11-08 2020-09-04 清华大学 一种混凝土仓内温差控制方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06193033A (ja) * 1992-12-25 1994-07-12 Ii R C:Kk マスコンクリート構造物の温度応力を部分加熱によって制御するコンクリート打設方法
JPH07119299A (ja) * 1992-08-07 1995-05-09 Ii R C:Kk マスコンクリート構造物のコンクリート打設方法

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07119299A (ja) * 1992-08-07 1995-05-09 Ii R C:Kk マスコンクリート構造物のコンクリート打設方法
JPH06193033A (ja) * 1992-12-25 1994-07-12 Ii R C:Kk マスコンクリート構造物の温度応力を部分加熱によって制御するコンクリート打設方法

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
M. Strauss, et al., Bureau of Reclamation, U.S. Department of the Interior, published 1949, "Cooling of Concrete Dams".
M. Strauss, et al., Bureau of Reclamation, U.S. Department of the Interior, published 1949, Cooling of Concrete Dams . *
T. Hirose et al., Dam Technology No. 28 published 1988, pp. 15 23, Method for Designing Temperature Control in RCD Method (with English summary). *
T. Hirose et al., Dam Technology No. 28 published 1988, pp. 15-23, "Method for Designing Temperature Control in RCD Method" (with English summary).

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6286271B1 (en) 1999-05-26 2001-09-11 Carl Cheung Tung Kong Load-bearing structural member
US20130269286A1 (en) * 2010-06-14 2013-10-17 Max Bögl Bauunternehmung GmbH & Co. KG Tower of a Wind Power Plant and Method for Producing a Tower of a Wind Power Plant
US9243418B2 (en) 2010-06-14 2016-01-26 Max Bogl Bauunternehmung Gmbh & Co. Kg Tower comprising an adapter piece and method for producing a tower comprising an adapter piece
US9091095B2 (en) * 2010-06-14 2015-07-28 Max Bogl Bauunternehmung Gmbh & Co. Kg Tower of a wind power plant and method for producing a tower of a wind power plant
CN102094528A (zh) * 2010-12-09 2011-06-15 中国葛洲坝集团股份有限公司 一种大体积混凝土冷却水管布置方法
CN102094528B (zh) * 2010-12-09 2012-01-18 中国葛洲坝集团股份有限公司 一种大体积混凝土冷却水管布置方法
WO2012075955A1 (zh) * 2010-12-09 2012-06-14 中国葛洲坝集团股份有限公司 一种大体积混凝土冷却水管布置方法
GB2496766A (en) * 2010-12-09 2013-05-22 China Gezhouba Group Co Ltd Method for arranging cooling water pipes in large volume concrete
GB2496766B (en) * 2010-12-09 2015-12-23 China Gezhouba Group Co Ltd Method for arranging cooling water pipes in mass concrete
CN102134911A (zh) * 2011-04-27 2011-07-27 河海大学 一种计算大体积混凝土水管冷却温度场的方法
CN102134911B (zh) * 2011-04-27 2012-05-09 河海大学 一种计算大体积混凝土水管冷却温度场的方法
JP2013023897A (ja) * 2011-07-20 2013-02-04 Kajima Corp コンクリートの養生方法
CN103410148B (zh) * 2013-05-29 2015-11-25 中建保华建筑有限责任公司 一种应用于基础底板混凝土浇筑的拦截网及其施工方法
CN103410148A (zh) * 2013-05-29 2013-11-27 中建保华建筑有限责任公司 一种应用于基础底板混凝土浇筑的拦截网及其施工方法
CN104131563A (zh) * 2014-07-30 2014-11-05 葛洲坝集团试验检测有限公司 一种大体积混凝土消应控制裂缝方法
CN105117567A (zh) * 2015-09-25 2015-12-02 福建江夏学院 一种新老混凝土黏结约束收缩有限元模型的构建方法
JP2018071217A (ja) * 2016-10-31 2018-05-10 鹿島建設株式会社 コンクリートの打設方法
CN108446438A (zh) * 2018-02-09 2018-08-24 广西交通科学研究院有限公司 刚构-拱组合桥成桥最优索力确定及快速实现方法
CN108981966A (zh) * 2018-07-02 2018-12-11 雷元新 一种大体积混凝土温度梯度限值分析方法及装置
CN108981966B (zh) * 2018-07-02 2020-08-25 雷元新 一种大体积混凝土温度梯度限值分析方法及装置
CN109056732A (zh) * 2018-09-18 2018-12-21 中水北方勘测设计研究有限责任公司 一种严寒地区混凝土高拱坝的温控方法
JP2020133102A (ja) * 2019-02-12 2020-08-31 りんかい日産建設株式会社 コンクリート打継部の評価方法および評価装置
CN111460545A (zh) * 2020-03-11 2020-07-28 华中科技大学 一种高效计算超高层结构温度应变的方法和系统
CN111460545B (zh) * 2020-03-11 2022-05-31 华中科技大学 一种高效计算超高层结构温度应变的方法和系统
CN112685818A (zh) * 2020-12-29 2021-04-20 武汉大学 混凝土拱坝坝体优化方法

Also Published As

Publication number Publication date
CN1125801A (zh) 1996-07-03

Similar Documents

Publication Publication Date Title
US5645773A (en) Method for placing concrete for construction of a master concrete structure
Klemczak et al. Early age thermal and shrinkage cracks in concrete structures–description of the problem
Jaafar et al. Development of finite element computer code for thermal analysis of roller compacted concrete dams
Zuo Bond strength of high relative rib area reinforcing bars
Burdet Analysis and design of anchorage zones in post-tensioned concrete bridges
Newell et al. Investigation of thermal behaviour of a hybrid precasted concrete floor using embedded sensors
Liu et al. Research on temperature action and cracking risk of steel–concrete composite girder during the hydration process
Liu et al. Sensitivity analysis of the early‐age cracking risk in an immersed tunnel
Van Tran et al. Prediction and control of temperature rise of massive reinforced concrete transfer slab with embedded cooling pipe
Nilimaa et al. Thermal crack risk of concrete structures: Evaluation of theoretical models for tunnels and bridges
Priestley The thermal response of concrete bridges
JPH0415346B2 (zh)
Rostásy et al. Assessment of external restraint
Mangold et al. Why are temperature-related criteria so unreliable for predicting thermal cracking at early ages
Thurston Thermal stresses in concrete structures.
Klemczak et al. External Restraint Factors in Early-Age Massive Foundation Slabs.
Anson et al. Early-age strain and temperature measurements in concrete tank walls
Flaga et al. Early-age thermal–shrinkage crack formation in bridge abutments–experiences and modelling
Ramsamooj Stresses in jointed rigid pavements
Hue et al. Öresund Bridge. Temperature and cracking control of the deck slab concrete at early ages
JP2000327450A (ja) コンクリート打設方法
Bamforth Concreting large-volume (mass) pours
Roy et al. Analysis of Massive Reinforced Concrete Ring Beam of Nuclear Containment Structure due to Heat of Hydration
Hemsley APPLICATION OF LARGE MATRIX INTERACTION ANALYSIS TO RAFT FOUNDATIONS.
Robins et al. Early-age finite element modelling of industrial ground floors

Legal Events

Date Code Title Description
AS Assignment

Owner name: E.R.C. CO., LTD., JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ICHIKAWA, YASUAKI;REEL/FRAME:007799/0393

Effective date: 19950605

REMI Maintenance fee reminder mailed
LAPS Lapse for failure to pay maintenance fees
FP Lapsed due to failure to pay maintenance fee

Effective date: 20010708

STCH Information on status: patent discontinuation

Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362